1. Field of the Invention
The present device relates to a speaker grille that is resin-molded from a synthetic resin and has a plurality of through holes, an injection molding mold, and to a broadcast data receiving device having such speaker grille.
2. Background Information
Generally, a speaker grille that covers the front of a speaker (such as an audio speaker) is provided with many through holes. When such speaker grilles is resin-molded by injection molding, distal end faces of mold pins on the stationary half of the mold are pressed at a specific pressure against the molding surface of the movable half. Then, the distal end faces of the mold pins are separated from the molding surface of the stationary half when the molded speaker grille is to be removed. If the through holes in the speaker grille are small in size, the length of the mold pins is greater than their diameter. Therefore, the mold pins tend to be misaligned or become deformed when the resin is cast into the mold, or when the molded speaker grille is taken out. Such misalignment and deformation result in aesthetic defects such as burrs in the through holes or in the surrounding areas. Another drawback is that repair of deformation of the mold pins drives up the cost. A number of inventions have been proposed to deal with this situation.
Japanese Patent Application Publication No. H5-50467 (paragraphs 0005 to 0021, FIG. 3) discusses a method for preventing burrs from being generated in the through holes and the surrounding areas, in the case of the injection molding a synthetic resin product that has an approximate V-shape in cross section with a roof portion and a side wall portion connected thereto, where a plurality of through holes are provided to the side wall portion that is at an angle relative to the roof portion. Since the side wall is at an angle relative to the roof portion, a gap is produced between the distal end force-cutting faces of the mold pins used to form the through holes and the movable half, and burrs tend to generated in this gap. According to the method disclosed in this document, the portion of the movable half that is pressed against the distal end faces of the mold pins and forms the areas around the openings of the through holes is formed in a stepped shape so as to be perpendicular to the through holes. In this manner, the gap between the distal end faces of the mold pins and the movable half against which these distal end faces are pressed is eliminated. Thus, no burrs are generated.
Japanese Patent Application Publication No. H7-117083 (paragraphs 0013 to 0035, FIGS. 4 and 6) discusses a method of preventing the occurrence of burrs or clogging in the through holes in the resin-molding of filters that have numerous through holes. According to this document, a plurality of protrusions corresponding to the through holes in the molded filter is provided to the movable half of the mold. Gas release holes and insertion holes are provided to the stationary half of the mold, so that the protrusions can be inserted into the insertion holes without any gap around the outer peripheral surface of the protrusions. After these protrusions are inserted into the insertion holes, the mold is clamped keeping the stationary and the movable halves of the mold apart by the thickness of the filter, and resin is injected into this gap. In this manner, occurrences of burrs and clogging in the through holes are prevented.
Japanese Patent No. 2,887,832 (paragraphs 0010 to 0030, FIGS. 1 and 2) discloses a method of preventing aesthetic defects such as flow marks and welds in the molding of a speaker grille that is designed cover the surface of a speaker. In the method of molding a speaker grille discussed in this document, a grille plate having a plurality of through holes and a frame provided around this plate are integrally resin-molded, and a ring-shaped groove is provided around the inner periphery of the frame between the frame and the grille plate. This structure allows the inside of the mold to be better filled with resin during the molding, and prevents generation of aesthetic defects such as flow marks and welds. The strength of the grille plate is also increased by integrally molding lattice-shaped reinforcing ribs on the back side of the speaker grille.
In Japanese Patent Application Publication No. H5-50467, the gap is eliminated between the distal end faces of the mold pins and the movable half, which helps to prevent generation of burrs. However, because the mold pins are shaped longer than their diameters, in other words the mold pins have a slender shape, there is no improvement in terms of the strength of the mold pins. Accordingly, misalignment or deformation of the mold pins is still likely to occur when the resin flows in.
In Japanese Patent Application Publication No. H7-117083, a plurality of protrusions corresponding to through holes to be formed in a molded article are provided to the movable half of the mold, and gas release holes and insertion holes are provided to the stationary half so that the protrusions could be inserted into the insertion holes without any gap between the protrusions and the insertion holes. Although this structure does prevent the clogging of the through holes, because the protrusions are shaped longer than their diameter in the case a filter having a small aperture size is molded, the strength of the protrusions cannot be sufficiently maintained. Accordingly, there is still a possibility that misalignment or deformation occurs when the resin flows in.
Although the technology of Japanese Patent No. 2,887,832 does prevent aesthetic defects such as flow marks and welds, the problem of aesthetic defects is not solved. When the through holes are formed so as to overlap with the reinforcing ribs that are formed in a lattice pattern on the back side of the speaker grille, the through holes appear to be clogged because the reinforcing ribs are visible through the through holes when viewed from the front of the speaker grille.
In addition to the methods discussed in the above documents, there is a method in which, rather than disposing the mold pins on just the stationary half of the mold, mold pins of the same shape are disposed on both the stationary half and the movable half as shown in FIG. 4. With this method, the strength of the mold pins is improved because the mold pins need to be only half as long as mold pins that are formed only on one of the movable and the stationary halves. However, if the mold pins provided on both sides are misaligned, or if the resin flows in between the joint faces of the mold pins because of inadequate pressure on the mold pins, burrs occur in the through holes and the surrounding areas as shown in FIGS. 4(c)-(d), and aesthetic defects result.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved speaker grille, injection molding mold, and broadcast data receiving device having such speaker grille that overcome the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.